In ETABS non-uniform loads can be assigned to shell elements via Assign>shell Loads>non Assign > Shell Loads > Non-uniform.
This option allows the user to assign non-uniform loads in any direction based on global coordinates.
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The load will have magnitude of 1000lb/ft . at the base and zero at top of the wall.
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Cz + D = 1000 at z = 0 ft
Cz + D = 0 0 at z = 12 ft
Solving the system above: D = 1000 and C = -83.33
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Total load = 1000*24*12/2=144000lbs or 144kips144,000 lbs or 144 kips
Reaction at top of the wall =144*4/12=48 kips or 24 kips at each support
Reaction at bottom of the wall=144*8/12= 96 kips or 48kips at each support
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